JP7021091B2 - Manufacturing method of tungsten oxide and tungsten mixed oxide - Google Patents

Description

The present invention relates to a method for producing a tungsten oxide powder by a flame spray pyrolysis method.

Tungsten trioxide is a known IR-absorbing substance that can also have good conductivity. Basically, such a mixed oxide prepares a solution containing a tungsten compound and, in some cases, a compound of a mixed oxide component, and subsequently removes the solvent and reduces the remaining solid. It is obtained by treating at a temperature of about 500 ° C. in the exerting atmosphere. Illustratively, European Patent Application Publication No. _18018115 (EP1801815), which includes the formula M xW _yOz (where M = alkali metal, 0.001 ≦ _x / y ≦ 1). The production of a tungsten mixed oxide of (1) and 2.2 (z / y≤3.0) is described. Powders so produced often exhibit poor dispersibility, eg, in coatings. Therefore, laborious pulverization and dispersion steps are often required.

In U.S. Patent Application Publication No. 2010/102700 (US2010 / 102700), a tungsten mixed oxide is produced by a flame spray pyrolysis method. At that time, the solution containing the tungsten compound and the compound of the mixed oxide component is put into a flame and oxidized there. However, only materials with a BET surface area of about 60-80 m ² / g are disclosed. Subsequent heat treatment of the material from the flame spray pyrolysis method to obtain sufficient crystallinity reduces the BET surface area to a value of about 20 m ² / g. This deteriorates the dispersibility.

A method that allows the production of tungsten oxide with high crystallinity and good dispersibility would be desirable.

The object of the present invention is a one-step and two-step production method of tungsten oxide or a tungsten mixed oxide. Both methods include flame spray pyrolysis.

Tungsten oxide powder or tungsten mixed oxide powder of the general formula M _x WO ₃ [in the formula, M = Na, K, Rb, Li and Cs, 0.1 ≦ x ≦ 0.5, preferably x = 0.33]. The two-step manufacturing method is a series of steps:
a) A step of preparing a solution containing tungsten and, in some cases, one or more compounds containing M at a concentration corresponding to a stoichiometric ratio M _x WO ₃ .
b) The step of spraying one or more solutions to form an aerosol in the reaction space,
c) The step of reacting the aerosol with a hydrogen flame / oxygen flame in the reaction space, where 1 <O _{2, primary} / 0.5H ₂ ≤ 3 holds for this flame.
Here the reaction space is configured to include two reaction regions with two different reaction mixture velocities v ₁ and v ₂ , where v ₂ = 0.3-0.8 v ₁ , preferably v ₂ =. 0.4 to 0.7 v ₁ and 0.5 ≤ v ₁ ≤ 10 Nm / s, preferably 1 ≤ v ₁ ≤ 5 Nm / s.
d) It comprises a step of separating a solid from a vaporous or gaseous substance, and e) a step of flowing a gas stream having a reducing action on the separated solid at a temperature of 450 to 700 ° C.

The BET surface area of the tungsten oxide powder produced by the method according to the present invention is 1 to 10 m ² / g.

The method according to the present invention preferably comprises WO ₃ , Li _0.33 WO ₃ , Na _0.33 WO ₃ , K _0.33 WO ₃ , Rb _0.33 WO ₃ , Cs _0.33 WO ₃ , and Cs _0. Suitable for the production of ₂₀ WO ₃ and Cs _0.25 WO ₃ . Similarly, a tungsten mixed oxidation of the general formula M _x1 M _x2 WO ₃ (here x1 + x2 = x) having not only tungsten but also two metals selected from the group of Na, K, Rb, Li and Cs. Material powders such as Na _0.1 K _0.1 WO ₃ can be produced.

The first reaction zone begins where the aerosol is introduced into the reaction space. The second reaction zone follows the first reaction zone. v ₁ is the average velocity in the first reaction zone and v ₂ is the average velocity in the second reaction zone. Here, v ₁ is larger than v ₂ . This can be achieved, for example, by making the cross-sectional area in the first reaction zone smaller. The calculations for v ₁ and v ₂ are based on the gas volume of the unreacted substance used, eg nitrogen or excess oxygen, and the gas volume of the product, substantially water vapor. For the description of speed, the normalized speed is used. This velocity is determined by dividing the volumetric flow with the unit of Nm ³ / h by the cross-sectional area.

The indication "O ₂ , primary" indicates oxygen in the air that produces the flame or, in some cases, oxygen-enriched air. Not only that, it would be rational to introduce additional air, secondary air, directly into the reaction space, apart from this air. The indication of "O ₂ , secondary" indicates oxygen in the secondary air. Here, it is preferable that the secondary air is sent so as to enter the reaction space for the first time in the reaction region 2.

Finally, spraying of the solution can also be done by air. The display of "O ₂ , spray" indicates oxygen in the spray air. Finally, the indication "O ₂ , ttl" represents total oxygen. It is best to choose the total oxygen to be 1.5 ≤ O _2, tl / 0.5H ₂ ≤ 5.

The ratio of O 2 _, tl / 0.5H ₂ or O _{2, primary} / 0.5H ₂ is based on the reaction of 2 mol of hydrogen with 1 mol of oxygen by 2H ₂ + O ₂ → 2H ₂ O.

Due to the features relating to O _{2, primary} / 0.5H ₂ and v ₂ = 0.4 to 0.8 v ₁ described in the claims, the temperature in the flame spray pyrolysis method is lowered to about 500 to 750 ° C. 1 A material with a surprisingly low BET surface area of ~ 20 m ² / g and already good crystallinity is produced.

It can be said that the BET surface area of the reduced material is smaller than the BET surface area of the material from the flame spray pyrolysis method. Normally, the BET _reduction / BET _FSP ratio is 0.60 to 0.95.

The hydrogen flame / oxygen flame that spreads in the reaction space is formed by igniting an oxygen-containing gas and a combustion gas that forms water in the reaction with oxygen.

In a particular embodiment, the average residence time of the reaction mixture in reaction zone 1 and reaction zone 2 is selected to be t ₂ > 0.5 t ₁ , preferably 0.7 t ₁ ≤ t ₂ ≤ 0.9 t ₁ . Here, t ₁ is the average residence time of the reaction mixture in the reaction region 1, and t ₂ is the average residence time of the reaction mixture in the reaction region 2.

The average residence time t ₁ is preferably 0.2 to 1 second, particularly preferably 0.3 to 0.7 seconds. The average residence time t ₂ is preferably 0.1 to 0.8 seconds, particularly preferably 0.2 to 0.5 seconds.

As the gas flow exerting the reducing action, hydrogen, a hydrogen / nitrogen mixture, or a hydrogen / rare gas mixture can be considered.

Not only a two-step method including a flame spray pyrolysis method and a subsequent reduction, but also a one-step method in which the reduction step can be omitted is a component of the present invention.

The object of the present invention is tungsten oxide powder or tungsten of the general formula M _x WO ₃ [in the formula, M = Na, K, Rb, Li and / or Cs, 0.1 ≦ x ≦ 0.5]. A one-step method for producing a mixed oxide powder, which is a series of steps:
a) A step of preparing a solution containing at least one tungsten compound and, in some cases, at least one M-containing compound at a concentration corresponding to a stoichiometric ratio M _x WO ₃ .
b) The step of spraying the solution to form an aerosol in the reaction space,
c) Reacting the aerosol with a hydrogen flame / oxygen flame with less than 1 lambda in the reaction space, where lambda = total oxygen / 0.5 × hydrogen, and d) vaporizing or d) solid. It is a manufacturing method including a step of separating from a gaseous substance.

An important feature of this method is that the lambda is less than one. This means that hydrogen and oxygen are selected so that there is a stoichiometrically excessive amount of hydrogen with respect to the reaction equation H ₂ + 0.5O ₂ → H ₂ O. Preferably, 0.6 ≦ lambda <1, particularly preferably 0.7 ≦ lambda ≦ 0.95, and extremely particularly preferably 0.8 ≦ lambda ≦ 0.9.

The average residence time in the reaction space is preferably 1-5 seconds for the one-step method.

In the method according to the invention, the fine droplets of solution are components of the aerosol. The fine droplets preferably have an average droplet diameter of less than 120 μm, particularly preferably 30-100 μm. Usually, one-component or multi-component nozzles are used to generate droplets.

The solution used shall have as high a concentration as possible. In doing so, the aim should be to optimize between the amount of powder produced and the material properties. For the method according to the invention, these requirements are 5 to 60% by weight, particularly preferably 25 to 55% by weight, very particularly preferably 30 to 50% by weight, based on the sum of W and M as metals, respectively. Best filled in the range.

The best results regarding powder homogeneity are obtained when tungsten compounds and alkali metal compounds are present in the solution. The solution can be heated to achieve solubility and to have a viscosity suitable for solution spraying. Basically, any soluble metal compound that can be an oxide under reaction conditions can be used. In this case, it may be an inorganic metal compound such as a nitrate, a chloride, a bromide, or an organic metal compound such as an alkoxide or a carboxylate. The use of nitrates can be particularly advantageous.

The organic solvent is preferably an alcohol such as methanol, ethanol, n-propanol, isopropanol, n-butanol or tert-butanol, diol such as ethanediol, pentanediol, 2-methyl-2,4-pentanediol, acetic acid, etc. Propionic acid, butanoic acid, hexanoic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, octanoic acid, 2-ethylhexanoic acid, valerian acid, capric acid or lauric acid can be used. In addition, benzene, toluene, naphtha and / or benzine can be used. Preferably, an aqueous solvent or water is used.

Examples 1 to 5 show the production of an alkali metal-tungsten-mixed oxide powder by a two-step method according to the present invention. Example 6 shows a comparative example of the two-step method. Examples 7-11 show the production of potassium-tungsten-mixed oxide powder by the one-step method according to the present invention.

Example 1
Prepare a solution of 2165 g of ammonium metatungstate, 335 g of cesium nitrate and 12.020 g of water. The total concentration of W and Cs as metals, respectively, is 12.7% by weight.

Reaction region 1: An aerosol is obtained by injecting this solution at 2500 g / h with 5 Nm ³ / h air as a nozzle injection gas at room temperature (23 ° C.) using a nozzle for two components. The aerosol is reacted with 8 Nm ^{3 / h (0.357 kmol / h) of hydrogen and 30 Nm 3 /} h of air (0.281 kmol / h of O ₂ ). The temperature 50 cm below the burner mouth is 527 ° C.

The residence time in the reaction region 1 is 0.48 seconds at a gas rate of 2.89 Nm / s.

Reaction region 2: Further, 15 Nm ³ / h secondary air (0.141 kmol / h O ₂ ) is introduced into the reactor outside the reaction region 1.

The residence time in the reaction region 2 is 0.36 seconds at a gas rate of 1.65 Nm / s. The reaction mixture is then cooled and the resulting solid is separated from the gaseous material in a filter.

This solid has a BET surface area of 7.2 m ² / g.

The solid from the FSP is heated to a final temperature of 500 ° C. under a nitrogen atmosphere at a heating rate of 8.0 ° C./min, where it is formed in a forming gas atmosphere (70/30) under a temperature of 500 ° C. for 2 hours. Process in volume% N ₂ / H ₂ , volume flow 100 Nl / h).

The resulting reduced solid has a BET surface area of 5.4 m ² / g. This solid dispersion (18% by weight in 1-methoxy-2-propanol) shows a dark blue color.

Examples 2 to 6 are carried out in the same manner. Example 6 is a comparative example in which the average speed is the same in both reaction regions. Table 1 shows the substances used and the reaction conditions. Table 2 shows the calculated values.

The two-step method according to the present invention is intended to obtain a material having a low BET surface area and already considerably high crystallinity in a flame thermal decomposition process. In the subsequent reduction step, the BET surface area is only slightly reduced while the reduction proceeds rapidly under mild conditions, and notably sintering does not occur. These materials are correspondingly well dispersible. In Comparative Example 6, a material with an increased BET surface area is obtained from the FSP. This material is less likely to reduce. The reduced material itself is less likely to disperse.

Example 7
Prepare a solution of 4316 g ammonium metatungstate, 502 g potassium acetate, 64 g glacial acetic acid and 4831 g water. The total concentration of W and K as metals, respectively, is 34.2% by weight.

An aerosol is obtained by injecting this solution at 9.0 kg / h with air at 9.2 Nm ³ / h as a nozzle injection gas at room temperature (23 ° C.) using a two-component nozzle. The aerosol is reacted with 10 Nm ³ / h hydrogen and 13.5 Nm ³ / h air. The temperature 50 cm below the burner mouth is 464 ° C. Lambda is 0.87. The residence time is 1.9 seconds.

The solid has a BET surface area of 2.4 m ² / g. This solid dispersion (18% by weight in 1-methoxy-2-propanol) shows a dark blue color. X-ray structural analysis revealed a hexagonal potassium-tungsten-mixed oxide.

Examples 8-11 are carried out in the same manner using the same solution. The reaction conditions are shown in Table 3.

Examples 7-11 show that the reduced powder can be produced by a one-step method, namely the flame spray pyrolysis method.

Claims (11)

A method for producing a tungsten oxide powder or a tungsten mixed oxide powder having the general formula M _x WO ₃ [in the formula, M = Na, K, Rb, Li and / or Cs, 0.1 ≦ x ≦ 0.5]. , A series of steps:
a) A solution containing at least one tungsten compound , or a solution containing at least one tungsten compound and at least one M-containing compound at a concentration corresponding to a chemical ratio of M _x WO ₃ . Preparation process,
b) The step of spraying the solution to form an aerosol in the reaction space,
c) A step of reacting the aerosol with a hydrogen flame / oxygen flame in the reaction space, where 1 <O _{2, primary} / 0.5H ₂ ≦ 3 holds for the flame.
Here, the reaction space is configured to include a reaction region 1 and a reaction region 2 having two different reaction mixture velocities v ₁ and v ₂ , respectively, wherein the cross-sectional area of the reaction region 1 is that of the reaction region 2. Smaller than the cross-sectional area, v ₂ = 0.3 to 0.8 v ₁ and 0.5 ≤ v ₁ ≤ 10 Nm / s.
d) The production method comprising a step of separating a solid from a vapor-like or gaseous substance, and e) a step of flowing a gas stream having a reducing action on the separated solid at a temperature of 450 to 700 ° C. 1.5 ≤ O _2, tl / 0.5H ₂ ≤ 5, and O ₂ , tl is the total oxygen of O 2, _primary , O _{2, secondary} , and O _{2, spray} .
O _{2 and secondary} are oxygen in the secondary air that enters the reaction space for the first time in the reaction region 2.
O _{2, The production method according to claim 1, wherein the spraying} is oxygen in the sprayed air. t ₂ > 0.5 t ₁
t ₁ is the average residence time of the reaction mixture in the reaction region 1.
The production method according to claim 1 or 2, wherein t ₂ is the average residence time of the reaction mixture in the reaction region 2. The production method according to any one of claims 1 to 3, wherein the heat treatment is carried out for 1 to 10 hours. The production method according to any one of claims 1 to 4, wherein a hydrogen, a hydrogen / nitrogen mixture or a hydrogen / rare gas mixture is used as the gas flow exerting the reducing action. Tungsten Oxide Powder or Method for Producing Tungsten Mixed Oxide Powder of General Formula M _x WO ₃ [in the formula, M = Na, K, Rb, and / or Li, 0.1 ≤ x ≤ 0.5] And a series of steps:
a) A solution containing at least one tungsten compound , or a solution containing at least one tungsten compound and at least one M-containing compound at a concentration corresponding to a stoichiometric ratio M _x WO ₃ . A step of preparing and having a concentration of 25-55 wt% based on the sum of W and M.
b) The step of spraying the solution to form an aerosol in the reaction space,
c) The step of reacting the aerosol with a hydrogen flame / oxygen flame having less than 1 lambda in the reaction space, where lambda = total oxygen / 0.5 × hydrogen, where the total oxygen is O _{2 , Primary} , O _{2, secondary} , and O _{2, total of sprays} ,
O _{2 and secondary} are oxygen in the secondary air that enters the reaction space for the first time in the reaction region 2.
O _{2, The production method comprising: spraying} is oxygen in the sprayed air, and d) separating a solid from a vaporous or gaseous substance. The production method according to any one of claims 1 to 6, wherein the average residence time in the reaction space is 1 to 5 seconds. The production method according to any one of claims 1 to 7, wherein the aerosol is sprayed using a one-component or multi-component nozzle, and the average droplet diameter of the aerosol is less than 120 μm. The production method according to any one of claims 1 to 8, wherein an inorganic metal compound is used as the tungsten compound and the M-containing compound. The production method according to any one of claims 1 to 9, wherein an aqueous solution is used as the solution. The production method according to any one of claims 1 to 5 , wherein the concentration of the metal in the solution is 5 to 60% by weight.